(a) Field of the Invention
The present invention relates to a planet carrier. More particularly, the present invention relates to a carrier cup of a planet carrier that improves strength thereof and reduces noise occurring in an automatic transmission by changing an interior circumferential shape of a leg.
(b) Description of the Related Art
An automatic transmission controls a hydraulic pressure by operating at least one solenoid valve according to a driving state, such as a vehicle speed and a throttle opening, in order to perform shifting to a target shift speed.
In order to automatically shift to a target shift speed, the automatic transmission includes at least one of planetary gear sets. Such a planetary gear set includes a sun gear, a ring gear, and a planet carrier as operational members thereof, and a plurality of pinion gears, engaged with the sun gear and the ring gear, are connected to the planet carrier.
In addition, planetary gear sets are divided into simple planetary gear sets and compound planetary gear sets, and the simple planetary gear sets are divided into single pinion planetary gear sets and double pinion planetary gear sets.
The single pinion planetary gear set is a planetary gear set where one type of pinion gears is engaged with the sun gear and the ring gear, and the double pinion planetary gear set is a planetary gear set where two types of pinion gears are engaged with each other, one of them being engaged with the sun gear and the other being engaged with the ring gear.
A conventional planet carrier includes a carrier cup and a carrier cover.
The carrier cover is provided with a carrier hole formed at a middle portion thereof, and the carrier cup is provided with a carrier hole corresponding to the carrier hole of the carrier cover. Therefore, the carrier cup is connected to the carrier cover by a carrier shaft inserted in the carrier holes.
In addition, a plurality of pinion holes is formed at the carrier cover and the carrier cup around the carrier holes, and pinion shafts are inserted respectively in the pinion holes. A pinion gear is rotatably mounted at the pinion shaft.
The carrier cup includes a carrier plate and a plurality of legs formed perpendicularly to the carrier plate. The leg has an arc shape and covers a part of an exterior circumference of the pinion gear.
According to the conventional carrier cup of the planet carrier, the leg covering the part of the exterior circumference of the pinion gear has a uniform thickness regardless of the shape of the exterior circumference of the pinion gear, and thus a distance between the exterior circumference of the pinion gear and an interior circumference of the leg is not uniform. Therefore, a tilt error of the pinion shaft that occurs when the carrier cup is not mounted perpendicularly to the carrier cover is substantial, and more particularly such tilt error is greater in the double pinion planet carrier where more than two pinion gears are mounted at one leg. In a case that rotational members of the planetary gear set are rotated, the tilt error is a major cause of noise occurring in the automatic transmission.
In addition, since the thickness of leg is uniform, it is hard to strengthen the leg.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.